During the process of laying up plies of unidirectional fiber reinforced pre-preg to form a composite laminate, such as a stiffener, wrinkles may sometimes form in one or more of the plies. Wrinkles are undesirable because they may result in voids or discontinuities in the cured laminate. Wrinkling may be due to, without limitation, a ply being deformed during the lay-up process and/or to relatively high friction between the unidirectional reinforcing fibers caused by the tackiness of the uncured resin. Wrinkling may be particularly problematic where a stack of unidirectional pre-preg plies is formed over a highly contoured tool surface.
In the past, in order to avoid wrinkling in contoured areas, pre-preg plies were cut into sections. The sections were then spliced together and individually placed on a contoured forming tool in order to achieve a desired curvature. However cutting and splicing the plies in this manner may have an undesirable effect on the properties of the cured part. In order to compensate for these potentially reduced properties, additional plies or doublers were sometimes required which may result in an increase in the thickness and weight of the stiffener. The cutting and splicing technique described above is also time consuming and labor intensive, results in material waste and may induce undesirable preload in the cured part. Also, when there is a need to add plies to the IML (inner mold line) it is necessary to add these plies gradually, at a specific rate, so that the contour of the IML is not too severe.
Accordingly, there is a need for a method and apparatus for fabricating highly contoured, fiber reinforced composite parts, such as stiffeners which may substantially reduce or eliminate ply wrinkling during the lay-up process, and which avoids the need for cutting and splicing plies.